False positive pregnancy test on birth control

Guest post by Stix who design and deliver pregnancy and ovulation tests during high-stress, high-stakes moments, to empower you with accurate, reliable results you need to make the right health choices.

In the 1970’s, Margaret Crane’s revolutionary invention of the at-home pregnancy test allowed women to find out if they are pregnant in the comfort of their own bathroom, without having to rely on a doctor and the pressures that came with it. Pregnancy tests have become the norm, with about 20 million sold per year in the US alone. Test results are extremely accurate, about 99% for a positive result.

The development of the pregnancy test was not just a feat of scientific advance, but it also granted women more information and agency over their bodies. That being said, there are still a lot of questions and uncertainty surrounding pregnancy tests, how to use them, and what your results mean.

We’re here today to clear the air on all things pregnancy tests and build a greater wealth of information for you and your body.  

How do pregnancy tests work?

Pregnancy tests work by detecting a hormone called hCG (human chorionic gonadotropin). Also known as the pregnancy hormone, hCG is produced when a fertilized egg attaches itself to the lining of the uterus and starts making a placenta to nourish itself. Traces of hCG start showing up in your urine at about 10 days after the egg is fertilized. For this reason, we recommend waiting 19 days after sex to take a test. Waiting to test is important, because the earlier you take the test, the harder it might be for the test to detect the surge in hCG.

If your test detects the hCG hormone, a positive result will display on the test window. The way your results are displayed will vary based on the brand you buy.

How soon can I take a pregnancy test for accurate results?

The answer to this question depends on the person—things like your menstrual cycle and the number of days since you last had sex can all be factors.

Most pregnancy tests are over 99% effective three days before your missed period. If your period isn’t regular (we feel you), wait at least 19 days after having sex to test. While it’s tempting to know as early as possible, a recent study on the pregnancy hormone shows that levels of hCG double every few days and your results will be more accurate the longer you wait. You're likely to get more accurate results, however, if you wait until after the first day of your missed period. To help time your pregnancy tests, try using a pregnancy test calculator to raise your chances of accurate results.

How do hormonal and non-hormonal birth controls affect pregnancy tests?

Good news: birth control does not interfere with the results of your pregnancy test.   As soon as you get pregnant, your body starts to produce a hormone called human chorionic gonadotropin (hCG). Pregnancy tests detect this hormone. Birth control hormones do not interfere with hCG. So if your period becomes irregular or is late, then you can use the test to check from pregnancy, even if you are on birth control.

How do you know when to test if you have an irregular period?

The good news is, you’re not alone. Over 30% of women have irregular periods. If you have an irregular period or your hormonal birth control has stopped your period, it’s best to test at least 19 days after having sex. At this point, if you are pregnant, your levels of hCG should be high enough to detect the pregnancy. If your periods are irregular and you want to accurately test for pregnancy, you might want to test more often.

What if I can't tell whether my pregnancy test is positive or negative?

Sometimes it can be hard to tell whether the test is positive or negative. There may be evaporation lines or confusing instructions that can lead your results to be inaccurate. To avoid this, read and follow the instructions on your test thoroughly and completely.

No matter how faint the line, if you see it, you are most likely pregnant. The faintness of the line can mean you are early in your pregnancy and your hCG levels are low.

The pregnancy test should have a control line that tells you whether the test was done correctly. If the control line is blank, then the test did not work and you should take another test.

What's a false positive pregnancy test?

Although not nearly as common as a false negative result, false-positive pregnancy test results do happen. A false positive pregnancy test is when you get a positive result from a home pregnancy test, but you’re not really pregnant.

A false positive result means that the pregnancy test detected the hormone hCG in your pee. For this to happen, either the test didn’t work right or you had hCG in your body for another reason. A number of factors can lead to a false-positive result including:

• Some medications, including fertility drugs that contain the hormone hCG
• Having an ectopic pregnancy or miscarriage
• Certain medical conditions
• Evaporation lines
• User error

What’s a false negative pregnancy test?

It is possible you could still be pregnant even if the test result is negative.

The accuracy of home pregnancy test results varies from woman to woman because:

• Sometimes menstruating individuals get false-negative results when they test too early in the pregnancy
• Each woman ovulates at a different time in her menstrual cycle
• The fertilized egg can implant in a woman's uterus at different times

If a test says you are not pregnant, take another pregnancy test in a few days. If you are pregnant, your hCG levels should double every 48 hours. If you think you are pregnant but more tests say you are not, call your doctor.

What can affect a pregnancy test?

It’s important not to drink too much of any liquid including water or alcohol before you take a pregnancy test. It’s better to wait until you naturally need to pass urine. This way, you’ll avoid diluting your level of pregnancy hormone and getting a false ‘Not Pregnant’ result.

Studies indicate that there are very few drugs (including cannabis) that affect the results of pregnancy tests - either positive or negative. However, fertility drugs containing hCG may interfere with home pregnancy test results by causing a false positive test result.

Is there a right time of day to take a pregnancy test?

The doctors we spoke to explained that taking a pregnancy test early in the morning helps avoid the chances of an incorrect result. This is because your urine is more concentrated when you wake up before drinking water, which makes it easier for pregnancy tests to detect hCG. However, when you're anxious to see results, it's understandable if you are tempted to test whatever time of day it is.

Will a pregnancy test be positive with an ectopic pregnancy?

An ectopic pregnancy happens when a fertilized egg implants itself somewhere outside the uterus, usually in the fallopian tubes. Unfortunately, ectopic pregnancies don’t develop into “normal” pregnancies, and instead are medical emergencies, as they can be harmful to your body.

Since ectopic pregnancies still produce the hormone hCG, they’ll register as a positive home pregnancy test. The telltale symptoms of an ectopic pregnancy (bleeding and abdominal pain) typically appear around 6-8 weeks.

While these questions cover a lot of information about pregnancy tests, they most certainly don’t cover everything. Feel free to comment down below any questions that may have popped up while reading this article or check out this resource to further help you understand pregnancy tests.
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